Method of making small to sub-miniature sizes of electric coils



Dec. 8, 1964 o N BLOOM METHOD OF MAKING SMALL TO SUB-MINIATURE SIZES 0F ELECTRIC COILS Filed Jan. 9, 1962 INVENTOR. Orro N. 51.00

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ATTORNEY ignite States Patent Z Y cc Fatented Dec. 8, 1054 This invention relates to the manufacture of electric coils such as are used in contractors, relays and solenoids, and more artieularly it relates to the manufacture of small, miniature and subminiature coils for the uses mentioned having substantially more ampere turns than standard coils, Without increase in over-all coil size.

This application is a continuation-in-part of my prior applicnti '1 Serial No. 651,226, filed April 8, 1957, and now abandone Prior to this invention the idea had largely prevailed in the coil art that while the bobbin could be quite thin, it should never be made so thin as to sacrifice the strength and rig ity required for supporting the winding. A typical expression of this attitude of rigid bobbins is the patent to Forrest et at, No. 2,856,639 (1958) disg a cementitious Omission of asion, as well c, while the s adds weight 22:1, expo 1g in mind, an important object of is to rovide a nod of making coils 1! above rein more ampere turns ovided than in prior coils wile be "tint objects of this invention hurling a coil of the kind I of all out-gnssingz substances. est of this invention is to provide a methcturing coils wherein the convolutions of s caused to after: to one another, without in5u!e...ng sheath of the wire or use of bindirther object of this invention is to provide of maki g coils wherein the coil is heat treated same by relieving all internal stresses in lltl its coating of insulation.

Yet another object of this invention is to provide a method of manufacturing coils wherein the resultant coil is sturdy and self-supporting without resorting to cements,

es or other binding material. or and further important objects of this invention be a parent from t..e disclosure in the accompanying drawzn and the spccifcation to follow.

In general, I accomplish the foregoing objects by windinc an insulated dry strand of wire, such as copper or aluminum, onto a specially designed bobbin of dielectric m rial, whi is so extremely thin that of itself it is cient to support the coil or even lend any material thereto. The coil so wound is then subjected to a heat treatment, preferably under vacuum, to relieve all stresses from the turns or convolutions of the windin and coincidentally to remove all substances therefrom that may liberate objectionable gases or contaminants during use of the coil and which might foul contact points when one or a set of such coils are used in a sealed compartment. Upon cooling to room temperature, the turns of the coil are found to adhere to one another, Without fusion or use of a binding material, suthciently to present a rigid, self-supporting coil.

The invention will now be set forth in detail in the following specification, to be read in conjunction with the accompanying drawing, in which:

FIGURE 1 depicts in elevation at special bobbin of a power coil manufactured according to the present invention;

FIGURE 2 is a view taken along line 2-2 of FIG- URE 1, looking in the direction of the arrows;

FIGURE 3 is an enlarged section taken along line 3-3 of FIGURE 2, looking in the direction of the arrows;

FIGURE 4 is an elevation of a form of bobbin holder employed in the winding and heat treatment of a coil;

FIGURE 5 shows a coil wound on its bobbin and the bobbin mounted on the holder of FIGURE 4, for placement in an oven for heat treatment;

FIGURE 6 is a erspective view of the complete coil according to the present invention, a portion of the outer covering or wrapping being broken away; and

FIGURE 7 is a perspective view of a modified coil produced according to the method of the present invention.

Aceordirg to the present invention, I first provide the bobbin or spool illustrated in FIGURES 1-3. This bobbin is comprised of a tubular cylinder 12, having an annular flange 10 mounted on each end thereof. It is impractical, if not impossible, to mold bobbins of the thinness conte a lated herein, and it is very (liti'icult and extensive to machine or grind bobbins down to the thickness here contemplated. Therefore I have devised the bobbin shown, and form same by first extruding the tubular cylinder 12 and cut same in lengths corresponding to the coil length desired. The flanges are stamped out of sheet material, and an opening is punched in the centers thereof. The edge portion about said opening is then flang d into a continuous cylindrical sleeve 14 for snugly fitting onto the cylinder 12, where-by a nice interfitting of the flanges on the cylinder is readily and Q lily acoinplished. As will be explained hereinafter, sleeve 14 is to become fixed to cylinder 12 during the winding of the coil thereon. In forming the sleeves on the flanges 14, as Well as in sliding snme onto the cylindcr, great care should be taken not to nick or crack the sleeve portion, as such flaw will lead to failure by hipotting when voltage is appnicd to the coil.

Both cylinder 12 and flanges 10 are composed of dielectric material which can be made extremely thin without having holes or electrically weakened portions therein. By the expressions designating the bobbin as extremely thin and of a strength insufficient in itself to support its winding, a thickness on the order of 0.001 to 0.006 of an inch is contemplated. In miniature coils, say inch outside diameter and inch long, the bobbin thickness should be on the order of 0.001 to 0.002 inch. However, for certain sub-miniature coils the thickness of the bobbin may be reduced to a mere film considerably less than 0.001 inch thickness, for the finished coils of this type often are no more than 0.020 inch in outside diameter and'0.050 in length. Since the bobbin affords no-or at most, negligiblesupport for its coil, in every case the minimum thickness of the material of the bobbin and of the insulation on wire 40 is limited only by the dielectric rating of the material.

obi is necessa extremely thin bo vironment the col order of 409 F., polyetetrafluorocthylene, availacle under the trader and other products of the iellon, will serve quite atisfactorily.

k :ocarbon family, For lower tem' eratures, nylon or My t .c'. equivalents, ma be employed.

For most small coils, \v're 4G is generally of AWG24-56 gauge, but it will be understood that the size of the wire should be varied to correspond with the duties of the particular coil. The wire 49 has been provisionally sheathed with insulation by passing same through a bath of one of the materials enumerated above or of insulating enamel. The diameter of such wire used in small coils, including insulation, is roughly .0021-006525 of an inch.

It may be mentioned at this point, that by reason of the extreme thinness of the bobbin herein disclosed, additional coil space is provided, and it is possible to wind more turns or wire thereon than is possible with a conventional thin" bobbin of the same over-all dimensions. in fact, in a bobbin according to the present invention, of 74 inch diameter and /2 inch length, wound with size AWG4O wire, from 500 to 600 additional turns of wire may be added over that of prior thin bobbins. This addition in ampere turns is reflected in increased pull-in strength of the coil, 1. i when the coil is used in a relay, many of the usual critical adjustments pert; ning to air gap at contact points, the armature spring, and the like formerly necessary in the man tacture of relays are obviated. This additional pull-in strength as added to the reliability of my coils under severe shocks and vibration, such as is encountered in ai -raft on missile systems. Conversely, in accor nce will. my invention, on a bobbin of the same over-all size of prior bobbins, I am able to apply the conventional number f urns of a size larger wire, thus increasing the ampere-turns without adding to the resistance of the coil.

cylinder 12 metal shaft or mandrel 3, ti of a unit 22 adapted to be anism. Unit 22 includes a rigid as part thereof, and an opposed si being adjustable along shaft 2%.

c, the latter threaded on thereof may be adjusted to position disks 2-4, .xed position contiguous flan es 1-3 of the bobbin. Disks 24 and 26 thus buttress and confine t flanges during the winding operation, and prevent bulg of the ends of the coil at this stage.

When the bobbin elements 13, 1.2 have bccn assembled on the mandrel 2G and the disks properly positioned with respect to the flanges of the bobbin, the sheathed wire 48 can be precision wound onto the bobbin in snug Contact. According to my method, the winding should be applied in what is known in the winding art as random fashion, in contrast to layer and honeycomb types of winding. In random fashion winding there is a limited cross-over of the turns or convolutions during traverse of the winding mechanism, establishing an interlock of the turns lengthwise the axis of the coil. This interlock comprises one of the important factors producing a wholly selfsustaining coil without resorting to fusion of the adjacent turns or use of space consuming binder materials.

In starting the Winding operation, as shown in FY- URE 4, the first run should begin at the edge of one of the sleeves 14 and continue back and forth between such edges until the winding has built up substantially even with the outer surface of the sleeves, whereupon the winding is extended over the sleeves on each traverse. As the winding begins to overlap the sleeves E4, the tension of the turns of wire causes the wirc to grip the sleeves 14, and the sleeves are thus compressed against the cylinder 12, becoming bound th' etc. A final wrapping 42 may then be applied to the coil and the ends of wire 4t} brought out for conventional terminal connections.

After winding and applying the final wrapping 42 to the coil, the unit 22, with the wound bobbin thereon, is placed in an oven, where it is subjected to a controlled temperature, preferably under vacuum, for a predetermined timc. The duration of the heat treatment may vary somewhat, depending upon the gauge of the wire and the number of turns, as well as the kind of wire and the material with which it is sheathed, and the temperature applied. For coils up to inch diameter and whic contain on the order of 6,000 turns of AWG40 wire on a Teflon bobbin and the wire also sheathed with the same material, I have found a temperature of substantially 375 F. should be maintained for a period of at least one hour, while optimum results are obtained at an hour and a half. For largegcoils the same heat and vacuum is applied, but the duration is prolonged in proportion to the size of the coil. Two hours of heating is sufficient for the larger coils.

The primary purpose of the heat treatment is to normalize or relieve the wire and its sheathing of the stresses induced in the winding operation, whereby the coil will tend to preserve its shape upon removal from the mandrel. The heat treatment, however, performs two further important functions: (1) It establishes a marked adherence of adjacent convolutions of the coil, which coupled with the random winding and the aforementioned normalizing of the coil, produces a rigid, sclfsustaining coil. (2) The heat treatment drives out substances picked up in the processing and handling of the wire, such as oils and other contaminants which otherwise would liberate gases apt to cause failure of the control mechanism of scaled units in which such coils are commonly used. These items will now be elaborated upon:

(1) My experience reveals that adherence of the convolutions of the coil may be effected at a temperature of 350 5., while the sheathing will stand a temperature of 375 F. without cold flow. Cold flow is known to designate the deformation or squeezing of insulation from between adjacent turns sufficient to permit contact of the wires and short circuiting at such areas of deformation. Since the optimum normalizing temperature is found to be at 375 F., I employ this temperature for both normalizing and obtaining adherence of the convolutions.

Concerning the adherence of convolutions effected by the aforementioned heat treatment, it is pointed out that during the heating both the mandrel and the coil expend, during which expansion the turns of wire are thought to press against one another and cause slight indentations or deformation of the contiguous sheathing. The 375 F. temperature is found to be precisely sufiicient to bring the turns of the coil into solid contact without reaching the stage of cold flow.

Regardless of whether the insulation on the wire be resin or enamel, the turns of the coil once brought into solid contact as herein described establish a marked adherence of the contiguous turns to one another. That is to say, thereafter it appears that a molecular force is exerted across the contacting surfaces of the many turns, normally retaining them, after cooling of the coil, in intimate relationship without bulging of the ends of the coil. The foregoing explanation of this phenomenon is fortified by the fact that after the Winding of the. coil on the mandrel and before the heat treatment, a wrench is needed to loosen nut 30; but after the heat treatment and the coil is allowed to cool, nut 30 can be removed with the fingers. N0 fusion of the turns together is involved, and no binder material is necessary nor used.

(2) In drawing of wire, some of the cutting oil and other substances adhere to the strand and other contaminants are picked up by a coil in the course of its handling in manufacture. These substances, when the coil is exoscd to a material increase in temperature, tend to volae and escape as a gashercin termed gassing. This may condense or otherwise accumulate on the conlfzcl points of a relay and cause failure of the system controlled thereby. Where several such devices are arranged in a scaled chamber the gas exuded from one coil may cause failure of the others, and when the coils are employed in a control for an airplane, for example, the result may be disastrous. It is therefore of utmost importance to drive out such gas liberating substances as may be incorporated in coils. I have found that this, too, is effectively accomplished in the aforementioned heat treatment, especially when carried out under vacuum at five microns or less at 375 F.

\Viiile the coils are under vacuum, an inert gas may be introduced into the vacuum oven for penetration into the coil upon relieving the vacuum. This inert gas should be bone dry, thereby avoiding any possibility of moisture entering the coil.

Following the heat treatment, the coil, while still on the mandrel, is allowed to cool slowly to room tcmperature, either while in the oven or removed therefrom. This normally takes about a half-hour. Too rapid heatmg or cooling of the coils may induce what is known as thermal shock, and damage or even ruin the coil. The heating and cooling cycles complete what, for lack of a better term, I term herein as normalizing of the coil. lly this term I designate the change within the wire resulting from the heating and cooling of the coil While still on the mandrel, whereby stresses in the coil, though to be by reason of rearrangement of the molecules, are completely relieved. The cooling results in a contraction and setting of the wire and its sheath into a final form. On removal from the mandrel 20 the coil will not expand or bulge at the endsv The coil dimensions remain precisely that of the inside length of the mandrel. With the elimination of bulging of the coil end by the present invention, when the ends of a coil are clamped during assembly in a relay frame, there is no compressive shear movement of the wire, with resultant broken wire and shorted turns.

As indicated above, in a coil produced according to the present invention. it is unnecessary that the bobbin be of sui'i cicnt strength to support or sustain the finished coil, [or wire 40, when wound and heat treated as herein d scribed results in a self-supporting or selhsustaining c 1. By the expression self-supporting or self-sustainis meant that the coil will retain its shape and conn without assistance from a bobbin for all reasonable a3, ..tior.s thereof. The bobbin, therefore, merely serves as a dielectric for and protector of the coil against abrasion. The flanges of the bobbin likewise do not buttress the coil, but serve only for the purpose just noted.

The fact that in my coil. the stresses within the wire have been completely relieved by said heat treatment, together with the adherence of the turns of the coil to one another, virtually eliminates wire breakage and cold flow, with resultant shorted turns and open circuits under all conditions of heat and vibration likely to be encountcred in use.

The coil of FIGURE 7 differs from that of FIGURE 6 only in that it is oblong in cross-scction.

While in the foregoing description certain details of my method have been set forth, it is to be understood that variations thereof may be made by those skilled in the art without departing from the scope of the invention as defined in the following claims.

int

I claim as my invention:

1. "he method of producing small and miniature selfsustaining relay coils, comprising providing a bobbin of dielectric material, having a thickness of not more than 0.006 inch, fitting said bobbin on a support having spaced buttress elements for the ends of said bobbin, random winding wire provisionally insulated with polytetrafiuoro ethylene onto said bobbin to form a coil, thereafter subjecting said coil while on said support to a dry heat treatment at a temperature on the order of 375 F. for not less than one hour to relieve substantially all internal stresses in said coil, thereafter allowing said support and coil to cool to room temperature, and finally removing the coil from said support.

2. A method of making compact small to sub-miniature sizes of self-supporting relay coils comprising providing a bobbin of dielectric material having a thickness not in excess of 0.006 inch, fitting said bobbin on a support having spaced parallehbuttress elements for the ends of said bobbin, random winding fine wire provisionally insulated with polytrafiuoroethylene onto said bobbin while on said support to form a coil, then subjecting said coil without fustion thereof or use of bonding material at a temperature on the order of 375 F. for a period of at least one hour to cause adherence of the turns of said coil without fusion thereof or use of banding material and to relieve internal stresses in the wire resulting from the winding operation, subsequently permitting said support coil to cool to room temperature, and finally removing the coil.

3. A method of making small, miniature and subminiature self-supporting relay coils comprising providing a bobbin of dielectric material having a thickness not in excess of 0.006 inch, said bobbin including a tubular cylinder and separate end flanges each flange including a sleeve fitted onto said cylinder, mounting said bobbin on a mandrel having buttress elements for the flanges of said bobbin, random winding fine wire provisionally insulntcd with polytetrafluoroethylcne onto said bobbin while on said mandrel, with the winding running onto said sleeves for gripping same against said cylinder in forming the coil, then subjecting said coil while retained on said mandrel to a dry heat treatment in an oven at a temperature on the order of 375 F. for a period of not less than one hour to remove any out-gassing substances from the coil, as well as to relieve the coil of all internal' stresses, thereafter and while still on the mandrel cooling said coil to room temperature, the heating and cooling effecting adherence of the turns of said coil to one another without fusion thereof or use of bonding materials.

References Cited by the Examiner UNITED STATES PATENTS OTHER REFERENCES Coilforrns of Nylon, Advertisement appearing in Fortune, June 1945.

JOHN F. CAMPBELL, Primary Examiner. 

3. A METHOD OF MAKING SMALL, MINIATURE AND SUBMINIATURE SELF-SUPPORTING RELAY COILS COMPRISING PROVIDING A BOBBIN OF DIELECTRIC MATERIAL HAVING A THICKNESS NOT IN EXCESS OF 0.006 INCH, SAID BOBBIN INCLUDING A TUBULAR CYLINDER AND SEPARATE END FLANGES EACH FLANGE INCLUDING A SLEEVE FITTED ONTO SAID CYLINDER, MOUNTING SAID BOBBIN ON A MANDREL HAVING BUTTRESS ELEMENTS FOR THE FLANGES OF SAID BOBBIN, RANDOM WINDING FINE WIRE PROVISIONALLY INSULATED WITH POLYTETRAFLUOROETHYLENE ONTO SAID BOBBIN WHILE ON SAID MANDREL, WITH THE WINDING RUNNING ONTO SAID SLEEVES FOR GRIPPING SAME AGAINST SAID CYLINDER IN FORMING THE COIL, THEN SUBJECTING SAID COIL WHILE RETAINED ON SAID MANDREL TO A DRY HEAT TREATMENT IN AN OVEN AT A TEMPERATURE ON THE ORDER OF 375* F. FOR A PERIOD OF NOT LESS THAN ONE HOUR TO REMOVE ANY OUT-GASSING SUBSTANCES FROM THE COIL, AS WELL AS TO RELIEVE THE COIL OF ALL INTERNAL STRESSES, THEREAFTER AND WHILE STILL ON THE MANDREL COOLING SAID COIL TO ROOM TEMPERATURE, THE HEATING AND COOLING EFFECTING ADHERENCE OF THE TURNS OF SAID COIL TO ONE ANOTHER WITHOUT FUSION THEREOF OR USE OF BONDING MATERIALS. 